Chest ACCP Career Connection
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

Guest Access | Sign In via User Name/Password
This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF) Free
Right arrow Submit a response
Right arrow Alert me when this article is cited
Right arrow Alert me when eLetters are posted
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Add to My Personal Article Archive
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Kalomenidis, I.
Right arrow Articles by Roussos, C.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Kalomenidis, I.
Right arrow Articles by Roussos, C.
(Chest. 2006;129:1259-1266.)
© 2006 American College of Chest Physicians

Angiopoietin-2 Levels Are Elevated in Exudative Pleural Effusions*

Ioannis Kalomenidis, MD; Androniki Kollintza, MSc; Ioanna Sigala, MD; Andreas Papapetropoulos, PhD; Spyros Papiris, MD, FCCP; Richard W. Light, MD, FCCP and Charis Roussos, MD, PhD, FCCP

* From the Marianthi Simou Laboratory (Drs. Kalomenidis, Sigala, Papiris, and Roussos, and Mrs. Kollintza), Department of Critical Care & Pulmonary Services, Athens Medical School, "Evangelismos" Hospital, Athens, Greece; the Department of Molecular Pharmacology (Dr. Papapetropoulos), School of Pharmacy, University of Patras, Patras, Greece; and the Department of Allergy, Pulmonary and Critical Care Medicine (Dr. Light), Vanderbilt University, Nashville, TN.

Correspondence to: Ioannis Kalomenidis, MD, Department of Critical Care and Pulmonary Services, Athens Medical School, "Evangelismos" Hospital, 45–47 Ipsilandou St, 10675 Athens, Greece; e-mail:jkalomenidis{at}hotmail.com

Abstract

Objective: To examine the pleural fluid (PF) and serum levels of angiopoietin (Ang)-1, Ang-2, and vascular endothelial growth factor (VEGF) in patients with pleural effusions (PEs).

Methods: One hundred fifteen patients, 16 with transudative PEs due to heart failure and 99 with exudative PEs (malignant, 40; para-pneumonic, 24; tuberculous, 13; miscellaneous etiologies, 22) were included in the study. PF and serum levels of the growth factors were measured using enzyme-linked immunosorbent assay.

Results: PF Ang-2 and VEGF levels but not Ang-1 levels were higher (p < 0.001) in exudates than in transudates. PF Ang-2 levels were higher in tuberculous PEs than in PEs of any other etiology and were lower in heart failure PEs than in PEs of any other etiology. The highest PF VEGF levels were observed in patients with malignant and parapneumonic PEs. The lowest PF VEGF levels were observed in patients with transudates. In PEs, Ang-2 levels correlate with VEGF levels (p < 0.001), RBC count (p = 0.002), nucleated cell count (p < 0.001), total protein levels (p < 0.001), and lactate dehydrogenase levels (p < 0.001). PF Ang-1 levels were lower than serum Ang-1 levels both in patients with exudates (p < 0.001) and in those with transudates (p = 0.001). PF Ang-2 levels were higher than serum Ang-2 levels both in patients with exudates (p < 0.001) and in those with transudates (p = 0.045). PF VEGF levels were higher than serum VEGF levels in patients with malignant PEs (p < 0.001) and parapneumonic PEs (p = 0.003), but lower than serum VEGF levels in heart failure PEs (p < 0.001). In patients with tuberculous PEs and exudative PEs of miscellaneous etiology, PF and serum VEGF levels did not differ significantly.

Conclusion: Ang-2 levels but not Ang-1 levels are elevated in exudative PEs, and they correlate with levels of VEGF and markers of pleural inflammation. It is thus possible that Ang-2 along with VEGF participate in pleural inflammation and the pathogenesis of exudative PEs.

Key Words: angiopoietins • exudates • pleural effusions • vascular endothelial growth factor • vascular hyperpermeability

Inflammation and associated vascular hyperpermeability resulting in plasma leakage are fundamental to the development of exudative, protein-rich pleural effusions (PEs).1 Increased permeability of the pleural microvasculature is generally attributed to factors that are released in inflammatory and malignant pleural diseases,1 although the exact pathogenetic mechanisms of exudative PEs are unclear. Vascular endothelial growth factor (VEGF) has been shown to play an important role in the formation of exudative PEs.2 Besides its proangiogenic properties, VEGF is a proinflammatory agent34 and a potent inducer of vascular hyperpermeability.5 VEGF levels are higher in pleural exudates than in transudates.6789 More importantly, VEGF blockage significantly reduces vascular permeability and pleural fluid (PF) accumulation in a murine model of malignant PE.1011

Angiopoietin (Ang)-1 and Ang-2 are receptor tyrosine kinase ligands that act in conjunction with VEGF in promoting angiogenesis occurring under both physiologic and disease conditions.12 In addition, in vivo studies1314 and in vitro studies151617 have demonstrated that Ang-1 has antiinflammatory and antipermeability properties; it blocks the expression of adhesion molecules on the endothelial cell surface, leukocyte adherence on endothelial cells and transmigration into tissues, and interleukin-8 production by endothelial cells. In addition, Ang-1 inhibits vascular permeability caused by VEGF and inflammatory agents. The effect of Ang-2 on inflammation and vascular permeability has not been examined as thoroughly. However, the observation that Ang-2 antagonizes the effects of Ang-1 in endothelial cells18 suggests that Ang-2 promotes vascular permeability. In line with this notion, Ang-2 destabilizes the endothelial cell monolayer integrity leading to the detachment of endothelial cells in vitro.19 More evidence supporting a hyperpermeability and proinflammatory function of Ang-2 comes from a recent in vivo study20 in which Ang-2 was found to induce edema formation and to exert a weak stimulatory effect on leukocyte migration when injected into a mouse paw.

The role of Ang in the pathogenesis of PEs has not been examined. The aim of the present study was to determine the levels of VEGF, Ang-1, and Ang-2 in PF and corresponding serum samples of patients with PEs. We hypothesized the following: (1) Ang-2 and VEGF levels, but not Ang-1 levels, are higher in exudative PEs than in transudative PEs; and that (2) Ang-2 and VEGF levels are higher in PF than in the corresponding serum samples in patients with pleural exudates but not in those with pleural transudates.

Materials and Methods

The study was approved by the Ethics Committee of our hospital, and every patient signed an informed consent form. Patients were prospectively recruited between March 2003 and December 2004. PEs were categorized as exudates or transudates according to the criteria of Light.21 A PE was attributed to heart failure when it was transudative, the patient had symptoms and signs of left ventricular failure, a heart ultrasound study revealed systolic or diastolic dysfunction of the left ventricle, and the PE responded to the appropriate therapy. A malignant PE was diagnosed if the PF cytology or pleural biopsy findings were positive (ie, proven malignant PE), or if the patient had a persistent PE and a known malignancy and alternative diagnoses were excluded (ie, probable malignant PE). A parapneumonic PE was defined as one associated with bacterial pneumonia, including empyema. A PE was categorized as tuberculous if Mycobacteria tuberculosis were found in PF, sputum, bronchial lavage fluid, or pleural biopsy specimen (positive smear or culture) [ie, proven tuberculous PE] or if pleural biopsy revealed granuloma and other granulomatous diseases were excluded (ie, probable tuberculous PE). A lymphocyte-predominant PE with no other explanation and with favorable response to antituberculous treatment was also considered to be of tuberculous origin. Other diagnoses were established based on clinical and laboratory data.

The PF was aspirated and blood was drawn immediately after the thoracentesis, and the specimens were collected in plain tubes. PF and blood samples were centrifuged at 1,000g at 4°C for 10 min. PF supernatants and serum samples were stored at –80°C. The following characteristics were recorded: PF and serum total protein levels; lactate dehydrogenase (LDH) concentration (upper limit for serum LDH, 480 IU/L); glucose levels; PF pH; PF RBC counts; PF nucleated cell counts; and differential cell counts. The levels of Ang-2 and VEGF in PE and serum were measured by enzyme-linked immunosorbent assay using a duoset methodology (R&D Systems; Minneapolis, MN). Ang-1 protein levels were measured by a sandwich noncompetitive enzyme-linked immunosorbent assay consisting of a primary mouse antihuman Ang-1 antibody and a secondary biotinylated goat antihuman Ang-1 antibody (both from R&D Systems). Streptavidin-HRP (R&D Systems) was used to amplify the antibody-antigen reaction, and the color was developed using a TMB-H2O2 kit (Pierce; Rockford, IL). Standard curves were generated using recombinant human Ang-1 protein (R&D Systems) at concentrations of 0 to 50 ng/mL. The minimum detectable dose of the assays for Ang-1, Ang-2, and VEGF were 200, 65, and 15 pg/mL, respectively.

Statistical Analysis
Values were reported as the median (interquartile range [IQR]) since they were found not to be normally distributed. Mann-Whitney, Kruskal-Wallis, and Wilcoxon ranked sum tests were used to assess the difference between different groups, as appropriate. The Spearman test was used to assess the correlation between variables. Values below the detection limit were assumed to be zero for statistical analysis. For statistical analysis, a statistical software package (SPSS, version 11.0; SPSS Inc; Chicago, IL) was used.

Results

Patient Characteristics
One hundred fifteen patients, 77 men and 38 women were included in the study. The median age was 68 years (IQR, 19 to 90 years). Sixteen patients had transudative PEs secondary to heart failure, and 99 patients had exudative PEs of different origin (Table 1 ): malignant PEs, 40 (proven, 32; probable, 8); parapneumonic PEs, 24 (empyemas, 4); tuberculous PEs, 13 (proven, 9; probable, 4); and pleural exudates of other etiologies, 22. A specific diagnosis could not be made in two patients after open pleural biopsy, and they were included in the "other exudates" group. A follow-up revealed that none of them had pleural disease 10 and 32 months after their discharge from the hospital. The PF and serum concentrations of Ang-1, Ang-2, and VEGF were measured in 103, 115, and 104 patients, respectively.


View this table:
[in this window]
[in a new window]

  		Table 1.. Laboratory Findings in Patients With PEs of Different Etiologies*

 
VEGF Levels in Patients With PEs
Detectable levels of VEGF were found in 103 of 104 serum samples and 99 of 104 PF samples. PF levels but not serum VEGF levels were significantly higher in patients with exudates than in those with transudates (Table 2 ). The highest PF VEGF levels were observed in patients with malignant or parapneumonic PEs, and the lowest PF VEGF levels were observed in patients with heart failure (Table 3 ).


View this table:
[in this window]
[in a new window]

  		Table 2.. PF and Serum Levels in Patients With Pleural Exudates and Pleural Transudates*

 

View this table:
[in this window]
[in a new window]

  		Table 3.. PF and Serum VEGF Levels in Patients With PEs of Different Etiologies*

 
PF VEGF levels did not correlate significantly with serum VEGF levels (p = 0.4). PF VEGF levels were significantly higher than the corresponding serum levels in patients with exudates but were significantly lower than the corresponding serum levels in patients with transudates (Table 2). When different patient groups were analyzed separately, PF VEGF levels were significantly higher than serum VEGF levels in patients with malignant or parapneumonic PEs (Table 3). Patients with tuberculous PEs or exudative PEs of miscellaneous etiologies had lower PF levels than serum VEGF levels, although the difference was not statistically significant (Table 3).

Ang-1 Levels in Patients With PEs
Detectable levels of Ang-1 were found in 100 of 103 serum samples and 68 of 103 PF samples. PF or serum Ang-1 levels did not differ significantly between patients with exudates and those with transudates (Table 2). PF or serum Ang-1 levels did not differ significantly among patients with PEs of different etiologies, although they tended to be higher in patients with heart failure (Table 4 ). PF Ang-1 levels did not correlate significantly with serum Ang-1 levels (p = 0.11). Serum Ang-1 levels were significantly higher than the corresponding PF levels both in patients with exudates and in those with transudates (Tables 2, 4).


View this table:
[in this window]
[in a new window]

  		Table 4.. PF and Serum Ang-1 Levels in Patients With PEs of Different Etiologies*

 
Ang-2 Levels in Patients With PEs
Detectable levels of Ang-2 were found in 105 of 115 serum and all PF samples (Fig 1 ). PF Ang-2 levels were significantly higher in patients with exudates than in those with transudates, while serum Ang-2 levels were significantly higher in patients with transudates than in those with exudates (Table 2). Patients with tuberculous pleuritis had significantly higher PF Ang-2 levels than patients with PEs of any other etiology (Table 5 ). On the other hand, patients with heart failure had significantly lower PF levels than patients with exudative PEs of any etiology (Table 5). The highest serum Ang-2 levels were observed in patients with heart failure, which were significantly different from the serum Ang-2 levels observed in other groups, except for patients with parapneumonic PEs or empyema (Table 5). PF Ang-2 levels did not correlate significantly with serum Ang-2 levels (p = 0.18). PF Ang-2 levels were significantly higher than the corresponding serum levels in patients with exudates, but were also higher than those with transudates (Tables 2, 5).


Figure 1
View larger version (15K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 1.. PF Ang-2 levels in patients with malignant PEs (MAL), parapneumonic PEs or empyema (PRP/EMP), tuberculous PEs (TBC), miscellaneous exudates (other), and heart failure (HF). Horizontal lines represent median values.

 

View this table:
[in this window]
[in a new window]

  		Table 5.. PF and Serum Ang-2 Levels in Patients With PEs of Different Etiologies*

 
Correlation Between PF Growth Factor Levels and PF Features
PF Ang-2 levels significantly correlated with PF VEGF levels (r = 0.36; p < 0.001). There was no significant correlation between PF Ang-1 levels and either PF Ang-2 levels (p = 0.92) or PF VEGF levels (p = 0.49). There was a significant inverse correlation between PF Ang-1 levels and either PF protein levels (r = –0.27; p = 0.026) [Fig 2 ] or PF/serum protein ratio (r = –0.21; p = 0.033). There was a positive correlation between PF Ang-2 levels and the following parameters: PF RBC count (r = 0.29; p = 0.002); PF nucleated cell count (r = 0.26; p = 0.006); PF protein levels (r = 0.5; p < 0.001); LDH levels (r = 0.46; p < 0.001); PF/serum protein ratio (r = 0.36; p < 0.001); and PF/serum LDH ratio (r = 0.47; p < 0.001). There was a marginally significant negative correlation between PF Ang-2 levels and PF pH (r = –0.19; p = 0.045). There was a significant positive correlation between PF VEGF levels and the following parameters: PF RBC count (r = 0.22; p = 0.003); PF protein levels (r = 0.38; p < 0.001); PF LDH levels (r = 0.6; p < 0.001); PF/serum protein ratio (r = 0.37; p < 0.001); and PF/serum LDH ratio (r = 0.61; p < 0.001). There was a negative correlation between PF VEGF levels and PF glucose levels (r = –0.36; p < 0.001), PF/serum glucose ratio (r = –0.44; p < 0.001), and PF pH (r = –0.036; p < 0.001).


Figure 2
View larger version (23K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 2.. Correlation between PF Ang-2 levels and PF total protein levels.

 
Discussion

In the present study, we determined the PF and serum concentrations of Ang-1, Ang-2, and VEGF in patients with PEs. This is the first report on PF levels of Ang-1 and Ang-2. Our main findings were as follows: (1) PF Ang-2 and VEGF levels but not Ang-1 levels were significantly higher in pleural exudates than in transudates; (2) PF Ang-2 levels were significantly higher than serum Ang-2 levels, and PF Ang-1 levels were significantly lower than serum Ang-1 levels both in patients with exudates and in those with transudates; PF VEGF levels were significantly higher than serum VEGF levels in patients with malignant PEs and parapneumonic PEs, but were significantly lower than serum VEGF levels in heart failure PEs; and (3) PF Ang-2 levels correlated with PF VEGF levels, PF RBC count, nucleated cell count, total protein levels, and LDH levels, and were inversely correlated with PF pH.

Pleural inflammation exists in a mutually dependent association with hyperpermeability of the pleural vasculature and constitutes the sine qua non for the pathogenetic basis of the vast majority of exudative PEs.1 On the other hand, transudative PEs, most commonly secondary to left heart failure, are formed as a result of fluid extravasation that is caused by a disruption of the equilibrium of hydrostatic and/or osmotic pressures across an intact endothelial membrane.22 The results of the present study confirmed previously made observations that the levels of VEGF, which is a factor that promotes vascular endothelial hyperpermeability and inflammation,345 were significantly higher in pleural exudates than in pleural transudates.6789 In agreement with data reported in previous studies,579 the highest PF VEGF levels were observed in malignant PEs and PEs secondary to bacterial infection. In addition, VEGF levels correlated with markers of vascular hyperpermeability and pleural inflammation, such as RBC count, PF protein level, PF/serum protein ratio, PF LDH levels, and PF/serum LDH ratio. We also have reported for the first time that there was a negative correlation between PF VEGF levels and PF pH as well as PF glucose levels. Both low PF pH and glucose levels are mainly due to increased metabolism in the pleural space, occurring in patients with pleural disease characterized by intense inflammation.23 Taken together, our findings support the hypothesis that VEGF is involved in the formation of exudative PEs.2

In agreement with previously reported data,789 PF VEGF levels were significantly higher than serum VEGF levels in patients with malignant and parapneumonic PEs or empyema, suggesting that VEGF is mainly produced locally in the pleural space affected by malignancy or bacterial infection. On the other hand, PF VEGF levels were lower than serum VEGF levels in patients with transudates. This finding suggests that in PEs due to heart failure, VEGF is not produced in the pleural cavity and that its presence in the PF is probably the result of diffusion from the blood. Interestingly, in patients with exudative PEs due to tuberculosis or miscellaneous etiologies, PF and serum VEGF levels did not differ significantly. The relationship between PF and serum VEGF levels in tuberculous PEs is controversial. Two studies89 have shown that VEGF concentration is significantly higher in PF than in serum, while Hamed and associates7 reported that PF and serum levels of the growth factor do not differ significantly. The reason for this discrepancy is unknown.

Ang-1 and Ang-2 have been shown2425 to be involved in the pathogenesis of a variety of human diseases including cancer, diabetic retinopathy, pulmonary hypertension, autoimmune arthritis, coronary artery disease, and primary biliary cirrhosis. Their role in pleural disease has not been examined before. In the present study, we demonstrated that PF levels of Ang-2, a factor that may exert hyperpermeability and proinflammatory functions,20 are significantly higher in exudative PEs than in transudative PEs due to heart failure, and that they correlate with markers of vascular hyperpermeability and pleural inflammation, such as PF RBC count, PF nucleated cell count, PF protein level, PF/serum protein ratio, PF LDH levels, PF/serum LDH ratio, and pH. The fact that PF Ang-2 levels correlated significantly with PF VEGF levels may suggest a functional association between these two growth factors in the pathogenesis of exudative PEs. Since VEGF induces Ang-2 up-regulation,26 we could speculate that Ang-2 may amplify the hyperpermeability and proinflammatory signal produced by VEGF. Interestingly, a significant correlation between Ang-2 and VEGF levels in peripheral blood has been reported in patients with diabetes mellitus,27 acute coronary syndrome,28 and heart failure.29 On the other hand, the observation that, in contrast to PF VEGF levels, Ang-2 levels were higher in tuberculous than in malignant and parapneumonic PEs may suggest that either VEGF or Ang-2 plays a primary role in the pathogenesis of pleural exudates of different etiologies.

PF Ang-2 levels were significantly higher than the corresponding serum levels in patients with exudates of different etiologies. This finding suggests that Ang-2 is locally produced in the pleural cavity in patient with malignant and inflammatory pleural diseases. Though the cellular origin of the growth factor in the pleural cavity was not examined in the present study, it is probable that Ang-2 is mainly produced by the endothelial and perivascular cells24 of the pleural microvasculature, since neither mesothelial nor inflammatory cells has been reported to express Ang-2. However, malignant cells may also produce Ang-2 in the pleural cavity since the up-regulation of Ang-2 expression is not uncommonly found in malignancies.30 Taken together, our data suggest that Ang-2 is produced locally in the pleural space, and may play a role in the promotion of pleural inflammation and hyperpermeability and participate in the formation of exudative PEs. Nevertheless, we would like to point out that the methodology of the current study does not permit definitive conclusions concerning this issue. Further studies, specifically designed to examine the functional significance of increased Ang-2 levels in exudative PEs are required.

Surprisingly, in contrast to the findings concerning PF VEGF levels, PF Ang-2 levels were marginally higher than the corresponding serum levels even in patients with transudative PEs due to heart failure. Since in patients with heart failure the PF mainly originates from the pulmonary vasculature,22 it is reasonable to assume that elevated Ang-2 levels in these PEs is the result of increased Ang-2 production from endothelial cells of pulmonary vasculature, although this scenario was not examined in the present study. However, this hypothesis is supported by the following: first, it has been shown that endothelial cells express Ang-2 when exposed to mechanical stress (ie, elevated pulmonary vein pressure occurring in left ventricular failure)31; second, patients with acute heart failure have been reported to have significantly higher peripheral blood Ang-2 levels than those with chronic heart failure, who, in turn, have significantly higher blood Ang-2 levels than healthy individuals29; and third, in our study, serum Ang-2 levels are higher in patients with PEs due to heart failure than in patients with pleural exudates, with the exception of those with malignancies.

Ang-1 was detectable in only 68 of 103 PF samples (66%), and Ang-1 levels did not differ significantly between exudative and transudative PEs. Furthermore, PF Ang-1 levels were significantly lower than the corresponding serum levels both in patients with exudates and in those with transudates. Moreover, PF Ang-1 levels do not differ between exudative and transudative PEs. All of the above indicate that Ang-1 is not produced in the pleural cavity in patients with either heart failure or pleural diseases characterized by inflammation and vascular hyperpermeability. Probably, the presence of Ang-1 in the pleural cavity is the result of diffusion from the blood. The finding that there was a negative correlation between PF Ang-1 levels and PF protein or PF/serum protein ratio, both of which are indexes of pleural vascular permeability, is in line with the previously reported data showing that Ang-1 is an antipermeability factor.1314 As for Ang-2, further in vivo studies are required to examine whether Ang-1 plays a role in the regulation of pleural permeability and the accumulation of PF.

What are the clinical implications of our findings? It looks rather impossible that the measurements of the PF levels of any of the examined growth factors could be used for diagnostic purposes since significant overlap between the diagnostic groups was found. This observation agrees with that of a recent study by Sack and associates,9 who showed that PF VEGF concentration is not a useful marker for diagnosing PEs. In contrast, we think that our results hold some, though still immature, therapeutic consequences. The finding concerning Ang-2 strongly encourages the conduct of further studies, which will use animal models in order to examine whether this growth factor is really a mediator of pleural inflammation and pleural vascular permeability, and whether it plays an important role in the pathogenesis of exudative PEs. If this proves to be true, it will provide a basis for the development of novel therapeutic strategies in which Ang-2 inhibitors may be used to treat patients with persistent exudative PEs.

In conclusion, Ang-2 levels, but not Ang-1 levels, are elevated in exudative PEs, and they correlate with levels of PF VEGF levels and markers of pleural inflammation, and with pleural vascular hyperpermeability. Thus, it is possible that Ang-2 along with VEGF participate in pleural inflammation and the formation of exudative PEs. Our observations call for further in vivo functional studies to elucidate the role of Ang in the pathogenesis of pleural diseases.

Footnotes

Abbreviations: Ang = angiopoietin; IQR = interquartile range; LDH = lactate dehydrogenase; PE = pleural effusion; PF = pleural fluid; VEGF = vascular endothelial growth factor

This research was supported by the "Thorax" Foundation, Athens, Greece.

Received for publication June 13, 2005. Accepted for publication October 22, 2005.

References

  1. Lee, YCG, Lane, KB (2003) Cytokines in pleural diseases. Light, RW Lee, YCG eds. Textbook of pleural disease. ,63-89 Arnold. London, UK:
  2. Grove, CS, Lee, YCG Vascular endothelial growth factor: the key mediator in pleural effusion formation. Curr Opin Pulm Med 2002;8,294-301[CrossRef][ISI][Medline]
  3. Detmar, M, Brown, LF, Schon, MP, et al Increased microvascular density and enhanced leukocyte rolling and adhesion in the skin of VEGF transgenic mice. J Invest Dermatol 1998;111,1-6[CrossRef][ISI][Medline]
  4. Kim, I, Moon, SO, Park, SK, et al Angiopoietin-1 reduces VEGF-stimulated leukocyte adhesion to endothelial cells by reducing ICAM-1, VCAM-1, and E-selectin expression. Circ Res 2001;89,477-479[Abstract/Free Full Text]
  5. Robberts, WG, Palade, GE Increased microvascular permeability and endothelial fenestration induced by vascular endothelial growth factor. J Cell Sci 1995;108,2369-2379[Abstract]
  6. Cheng, D, Lee, YCG, Rogers, JT, et al Vascular endothelial growth factor level correlates with transforming growth factor-ß isoform levels in pleural effusions. Chest 2000;118,1747-1753[Medline]
  7. Hamed, EA, El-Noweihi, AM, Mohamed, AZ, et al Vasoactive mediators (VEGF and TNF-{alpha}) in patients with malignant and tuberculous pleural effusions. Respirology 2004;9,81-86[CrossRef][ISI][Medline]
  8. Momi, H, Matsuyama, W, Inoue, K, et al Vascular endothelial growth factor and proinflammatory cytokines in pleural effusions. Respir Med 2002;96,817-822[CrossRef][ISI][Medline]
  9. Sack, U, Hoffman, M, Zhao, XJ, et al Vascular endothelial growth factor in pleural effusions of different origin. Eur Respir J 2005;25,600-604[Abstract/Free Full Text]
  10. Yano, S, Shinohara, H, Herbst, RS, et al Production of experimental malignant pleural effusions is dependent on invasion of the pleura and expression of vascular endothelial growth factor/vascular permeability factor by human lung cancer cells. Am J Pathol 2000;157,1893-1903[Abstract/Free Full Text]
  11. Yano, S, Herbst, RS, Shinohara, H, et al Treatment for malignant pleural effusion of human lung adenocarcinoma by inhibition of vascular endothelial growth factor receptor tyrosine kinase phosphorylation. Clin Cancer Res 2000;6,957-965[Abstract/Free Full Text]
  12. Tsigkos, S, Koutsilieris, M, Papapetropoulos, A Angiopoietins in angiogenesis and beyond. Expert Opin Investig Drugs 2003;12,933-941[CrossRef][ISI][Medline]
  13. Thurston, G, Rudge, JS, Ioffe, E, et al Angiopoietin-1 protects the adult vasculature against plasma leakage. Nat Med 2000;6,460-463[CrossRef][ISI][Medline]
  14. Thurston, G, Suri, C, Smith, K, et al Leakage-resistant blood vessels in mice transgenically overexpressing angiopoietin-1. Science 1999;286,2511-2514[Abstract/Free Full Text]
  15. Kim, I, Moon, SO, Park, SK, et al Angiopoietin-1 reduces VEGF-stimulated leukocyte adhesion to endothelial cells by reducing ICAM-1, VCAM-1, and E-selectin expression. Circ Res 2001;89,477-479[Abstract/Free Full Text]
  16. Gamble, JR, Drew, J, Trezise, L, et al Angiopoietin-1 is an antipermeability and anti-inflammatory agent in vitro and targets cell junctions. Circ Res 2000;87,603-607[Abstract/Free Full Text]
  17. Pizurki, L, Zhou, Z, Glynos, K, et al Angiopoietin-1 inhibits endothelial permeability, neutrophil adherence and IL-8 production. Br J Pharmacol 2003;139,329-336[CrossRef][ISI][Medline]
  18. Maisonpierre, PC, Suri, C, Jones, PF, et al Angiopoietin-2, a natural antagonist for Tie2 that disrupts in vivo angiogenesis. Science 1997;277,55-60[Abstract/Free Full Text]
  19. Scharpfenecker, M, Fiedler, U, Reiss, Y, et al The tie-2 ligand angiopoietin-2 destabilizes quiescent endothelium through an internal autocrine loop mechanism. J Cell Sci 2005;118,771-780[Abstract/Free Full Text]
  20. Roviezzo, F, Tsigkos, S, Kotanidou, A, et al Angiopoietin-2 causes inflammation in vivo by promoting vascular leakage. J Pharmacol Exp Ther 2005;314,738-744[Abstract/Free Full Text]
  21. Light, WR, MacGregor, MI, Luchsinger, PC, et al Pleural effusions: the diagnostic separation of transudations and exudates. Ann Intern Med 1972;77,507-514[ISI][Medline]
  22. Light, RW Chapter 2. Physiology of the pleural space. Pleural diseases. 4th ed. 2001,8-20 Lippincott Williams & Wilkins. Philadelphia, PA:
  23. Light, RW Chapter 4. Clinical manifestations and useful tests. Pleural diseases 4th ed. 2001,42-86 Lippincott Williams & Wilkins. Philadelphia, PA:
  24. Jones, FP Not just angiogenesis-wider roles for the angiopoietins. J Pathol 2003;201,515-527[CrossRef][ISI][Medline]
  25. Medina, J, Sanz-Cameno, P, Garcia-Buey, L, et al Evidence of angiogenesis in primary cirrhosis: an immunohistochemical descriptive study. J Hepatol 2005;42,124-131[ISI][Medline]
  26. Mandriota, SJ, Pepper, MS Regulation of angiopoietin-2 mRNA levels in bovine microvascular endothelial cells by cytokines and hypoxia. Circ Res 1998;83,852-859[ISI][Medline]
  27. Lim, HS, Lip, GYH, Blann, AD Angiopoietin-1 and angiopoietin-2 in diabetes mellitus: relationship to VEGF, glycaemic control, endothelial damage/dysfunction and atherosclerosis. Atherosclerosis 2005;180,113-118[CrossRef][ISI][Medline]
  28. Nadar, SK, Blann, AD, Lip, GYH Plasma and platelet-derived vascular endothelial growth factor and angiopoietin-1 in hypertension: effects of antihypertensive therapy. J Intern Med 2004;256,331-337[CrossRef][ISI][Medline]
  29. Chong, AY, Caine, GJ, Freestone, B, et al Plasma angiopoietin-1, angiopoietin-2 and angiopoietin receptor tie-2 levels in congestive heart failure. J Am Coll Cardiol 2004;43,423-428[Abstract/Free Full Text]
  30. Takanami, I Overexpression of Ang-2 mRNA in non-small cell lung cancer: association with angiogenesis and poor prognosis. Oncol Rep 2004;12,849-853[ISI][Medline]
  31. Chang, H, Wang, BW, Kuan, P, et al Cyclical mechanical stretch enhances angiopoietin-2 and Tie2 receptor expression in cultured human umbilical vein endothelial cells. Clin Sci 2003;104,421-428[CrossRef][ISI][Medline]




This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF) Free
Right arrow Submit a response
Right arrow Alert me when this article is cited
Right arrow Alert me when eLetters are posted
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Add to My Personal Article Archive
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Kalomenidis, I.
Right arrow Articles by Roussos, C.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Kalomenidis, I.
Right arrow Articles by Roussos, C.

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS